Many portable or mobile devices comprise a battery, which acts as a power source for the device. As performance of the device increases, requirements of the battery increase. It should be charged fast and effectively. Some devices use different kind of fast charging solutions, for example with charging power of more than 15 W. Even with relatively high efficiency, there is still a considerable thermal impact. The devices may heat up during the charging process. The end-user may feel that the device is uncomfortably hot. It is also possible that the device has heated up internally so much that the performance of the device may deteriorate.